Add more comments.
Changed return value for HDFS'es fallocate.
Removed unnecessary code in ColumnBufferCompressed::writeToFile
Replaced Nulls with Empties in variable names.
Fixes the following:
* Compression ratio calculation was incorrect
* Possible issues due to system catalog thread ID usage
* Compressed file size data count was leaking many FDs when the table
wasn't compressed
* Compressed file size data count was allocating random large amounts
of RAM and then leaking it when the table wasn't compressed
* Add INFORMATION_SCHEMA.COLUMNSTORE_FILES which contains information
about files
* Remove file information from COLUMNSTORE_EXTENTS (due to above)
* Hide columns with Object ID < 3000 (internal columns)
* Fix bad calculation in data_size columns
* Fix minor memory leak
* Add compressedSize() function to IDBFileSystem to get the used file
size for a compressed file
* Add columnstore_info schema with utility stored procedures to access
the information_schema tables
